The transport mechanism and selectivity of divalent cation transport catalyzed by ionophore A23187 and 12 derivatives will be studied. Alterations in the transport selectivity pattern arising from systematic variations in membrane composition and the presence of novel phospholipids and lipid analogs will be studied. The work is divided into two categories: 1) equilibrium and kinetic complexation studies in methanol-water solvents, and 2) transport selectivity and mechanism studies in methanolliposome-aqueous biophasic media. 1) In homogenous solutions of methanol-water mixtures (0-95% w/w) equilibrium protonation constants and stepwise binding constants for divalent cations will be determined. The roles of protonation state, solvent properties and cation complexation on the conformation of A23187 and derivatives will be studied. Fast reaction techniques will be employed to study the individual ionophore divalent cation reactions relevant to the transport process. Factors affecting the detailed mechanism of A23187-cation formation and dissociation reactions will be investigated. 2) In aqueous media containing unilaminar liposomes the transport selectivity pattern of A23187 and derivatives will be determined. Variations in the pattern and absolute transport velocities resulting from compositional variation of the extra- and intra-liposomal media will be studied. The effect of membrane surface charge, phospholipid polar group structure and membrane cholesterol content on transport parameters will be investigated. Alterations in transport specificity resulting from the plasmalogen, ether and diol phospholipids will be studied. The mechanistic basis of observed selectivity patterns will be analyzed in terms of the individual reaction steps comprising the overall transport process and in terms of the steady state levels of individual ionophore species under transport conditions.